Gaseous sealing means in an apparatus for working materials by a beam of charged particles



l ml 3;. 3 j btrmm nuuw Nov. 10, 1964 F. w. BARRY 3,156,811

GASEOUS SEALING MEANS IN AN APPARATUS FOR WORKING MATERIALS BY A BEAM OFCHARGED PARTICLES Filed Nov. 5, 1962 4 Sheets-Sheet l IN VEN TOR.

ATTUQNEYS mm v Nov. 10, 1964 F. w. BARRY 3,156,811

GASEOUS SEALING MEANS IN AN APPARATUS FOR WORKING MATERIALS BY A BEAM OFCHARGED PARTICLES Filed Nov. 5, 1962 4 Sheets-Sheet 2 FIG. 2

Nov. 10, 1964 F w BARRY 3,156,811

GASEOUS SEALING MEAIiS IN AN APPARATUS FOR WORKING MATERIALS BY A BEAMOF CHARGED PARTICLES Filed Nov. 5, 1962 4 Sheets-Sheet 3 FIGB 210 l mu"1/ 2oo 22s uz AMA Nov. 10, 1964 F. w. BARRY 3,156,311

GASEOUS SEALING MEANS IN AN APPARATUS FOR WORKING MATERIALS BY A BEAM OFCHARGED PARTICLES Filed Nov. 5, 1962 4 Sheets-Sheet 4 United StatesPatent 3,156,811 GASEOUS SEALING MEANS IN AN APPARATUS FOR WORKINGMATERIALS BY A BEAM 0F CHARGED PARTICLES Frank W. Barry, Manchester,Conn., assignor to United Aircraft Corporation, East Hartford, Conn., acorporation of Delaware Filed Nov. 5, 1962, Ser. No. 235,214 22. Claims.(Cl. 219121) This invention relates to the working of materials, forexample, drilling, welding or surface treating, by means of a beam ofcharged particles or the like. In the apparatus to be described aprecisely focused beam of electrons impinges upon the material to beworked and the energy thereof works the material.

Among the advantages of using an electron beam or the like areinertialess control and great energy concentration. The chiefdisadvantages include the tendency for an electron beam to scatter andattenuate upon contact with air or other material.

One obvious means for avoiding such attenuation and scattering is toenclose the electron beam generator and the material to be worked in avacuum. This approach, however, entails obvious disadvantages. First,there is a serious work size limitation imposed by the dimensions of anevacuated work chamber. Secondly, rapid vaporization of the materialbeing worked is encountered and the vaporized work material is depositedon the inside of the apparatus with a cloud of vaporized materialcausing some attenuation of the beam.

In order to avoid the last-mentioned difliculty, the work may beenclosed in an inert atmosphere to minimize vaporization of the materialbeing worked. It will be apparent however, that any environmental gaswill cause attenuation of the electron beam in proportion to thepressure of the gas. To minimize such attenuation, two devices have beenutilized in the past.

First, the work chamber has been sealed oil. from the evacuated vesselwhich contains the electron beam. This approach necessitates theprovision of a window in the path of the beam which window is nonporousto an environmental gas at roughly atmospheric pressure but which istransparent with respect to the electron beam. It has been found that awindow material meeting the former requirement will so attenuate thebeam as to require an economically prohibitive power input to operatethe beam generator. Moreover, the window material itself will vaporizeon contact with the beam at the power levels required to work materials.

A second device which has been utilized to minimize beam attenuationcomprises a so-called dynamic pressure stage-stretch. A small diameterbore is provided interconnecting an evacuated beam chamber and a workchamber and the pressure stage stretch minimizes attenuation of the beamin passage through the bore. The stretch includes a system of pressurecascade chambers of increasmg gas pressures which are arranged in seriesin the direction of beam and also includes fine aligned apertures sothat only a fraction of the total pressure difference will be effectiveto cause the work chamber gas to enter each successive chamber. Theelectron beam can be conducted through these apertures and thus, stageby stage, from that portion of the evacuated chamber containing the beamgenerator into chambers of progressively higher gas pressure and finallyinto the work chamber. This approach has been used in the art ofelectron microscopy but like the electron beam window approach, itcauses excessive attenuation of the beam at the relatively high energyconcentrations required for working materials. Further,

3,156,811 Patented Nov. 10, 1964 extensive pumping means are required tomaintain the low pressures in the various pressure chambers.

The general object of the present invention is to prevent gas adjacent aworkpiece from flowing into an evacuated beam vessel or chamber by meansof a stream of sealing gas discharged adjacent the vessel or chamberopening.

Another object is to so direct a stream of sealing gas that a stream ofrelatively low total pressure can be used to prevent workpieceenvironmental gas from flowing into an evacuated beam vessel, thusminimizing leakage of the sealing gas into said vessel.

Another object is to achieve a pressure gradient across a stream ofsealing gas by turning the same just prior to discharge from a supplypassageway, thus further minimizing the leakage of sealing gas into thevessel.

Still another object is to achieve a more pronounced pressure gradientacross a stream of sealing gas by the use of a convergent-divergentnozzle to achieve supersonic flow adjacent a vacuum vessel opening thusrealizing a lower pressure in that region of the sealing gas stream andthus minimizing still further the leakage of sealing gas into thevessel.

Still another and a more specific object is to provide a gaseous sealacross an evacuated vessel opening by directing a stream of sealing gasacross a beam, the attenuation of the beam due to the sealing gas beingminimized by the low total pressure of the gas and the short path of thebeam in traversing the gas stream.

Still another specific object is to provide a gaseous seal around theperiphery of a vessel opening by directing a stream of sealing gasgenerally radially outwardly with respect to the beam and adjacent aworkpiece.

Still another specific object is to provide a mechanical seal around theperiphery of a gaseously sealed vessel opening whereby to reduce stillfurther the leakage of sealing gas into the vessel.

The drawings show four embodiments of the invention and such embodimentswill be described, but it will be understood that various changes may bemade from the constructions disclosed, and that the drawings and description are not to be construed as defining or limiting the scope ofthe invention, the claims forming a part of this specification beingrelied upon for that purpose.

Of the drawings:

FIG. 1 is a schematic cross sectional view of one embodiment of myinvention wherein a two dimensional rectangular passageway directs asupersonic stream of sealing gas into a beam chamber generallytransversely with respect to the beam and which stream is shownrecaptured in a supersonic diffuser.

FIG. 2 is a schematic cross sectional view of a second embodiment of myinvention wherein an annular passageway directs the sealing gas int-o abeam chamber generally obliquely with respect to the beam, said sealinggas being ultimately discharged into the environmental gas surroundingthe workpiece.

FIG. 3 is a schematic cross sectional view of a third embodiment of myinvention wherein an annular passageway directs the supersonic stream ofsealing gas generally radially outwardly with respect to the beamdirectly into the environmental gas.

FIG. 4 is a schematic cross sectional view of a fourth embodiment of myinvention, similar to that depicted in FIG. 3 but also including amechanical seal around the beam.

Gaseous Seal Across Beam, Closed Loop System, FIG. 1

Referring to FIG. 1, a beam generator 10 is shown emitting a beam alongan axis 12, which beam is concentrated by a focusing means 14, 14 to bepassed through a small vessel opening 16 into a beam chamber 18 andthence through a second opening 20, aligned with the vessel opening 16,to impinge on a workpiece 50 supported on a table or other worksupporting or holding means 51. It should, of course, be understood thatbeam generator is shown schematically. For a complete disclosure of astate-of-the-art electron beam generator of the type being employed incommercially available welding and cutting machines and typical of thosewith which this invention is intended for use, reference is made to US.Patent No. 2,987,610, issued June 6, 1961, to K. H. Steigerwald. Asexplained above, it is an object of this invention to obviate thenecessity of utilizing an evacuated work chamber, such as chamber 24 ofFIG- URE 1 of the Steigerwald patent, when working materials with anintense beam of charged particles.

Although the focusing means shown comprises a magnetic lens, anysuitable focusing means may be employed. For example, a series ofelectric lenses comprising an electrostatic focusing system is alsowithin the scope of this invention.

That part of the beam generator 10 from which the beam emanates iscontained in an evacuated vessel 22 connected by piping means 24 to ahigh vacuum pump 26. The pump 26 is capable of maintaining a pressure onthe order of 10- Torr in the evacuated vessel 22.

Although the vessel opening 16 is shown in the evacuated vessel 22 saidopening may be defined in the last chamber in a pressure stage stretchif both this invention and a stretch were to be combined in oneapparatus.

Interposed between the workpiece 50 and the evacuated vessel 22, andattached to the latter in the schematic view of FIG. 1 is a housingmeans 30 comprising internally opposed wall surfaces 32 and 34. Thesurfaces 32 and 34 are arranged in inner to outer order with respect tothe vessel opening 16 and at least partially define a gas supplypassageway 33. An inlet end of the passageway 33 is connected by pipingto a pressurized source of sealing gas 28 and the outlet end 17 thereofis connected to and communicates with the beam chamber 18.

Said housing means also comprises the internally opposed wall surfaces42 and 44 arranged in inner to outer order with respect to the vesselopening 16. The surfaces 42 and 44 at least partially define a returnpassageway 43 for the sealing gas, the inlet end 19 of the returnpassageway outlet communicating with the opposite side of the beamchamber 18. The outlet end of the return passageway 43 may be connectedto the source 28 by piping means 46 as illustrated.

As shown the housing 30 is subadjacent the evacuated vessel 22 but thisarrangement is intended to be merely exemplary and the vessel 22 shouldbe taken as representative of any chamber or series of chambers theoutermost of which is in communication with the workpiece environmentthrough an opening such as 16 and which is at some pressure less thanthat of the workpiece environmental gas.

The supply passageway 33 may take various forms but is shown as beinggenerally rectangular whereby conveniently to illustrate twodimensionally the flow of sealing gas therein. As shown in FIG. 1 thesupply passageway 33 turns the stream of sealing gas generally towardthe vessel opening 16 by means of the generally concave outer wallsurface 34. In turning the stream a pressure gradient is achievedthereacross, the lower pressure resulting in that part of the dischargedstream adjacent the vessel opening 16.

In order to reduce still further the pressure of the Sealing gas in thearea of the vessel opening 16 a nozzle is preferably employed toincrease the velocity of the stream. As shown a supersonic nozzle meansis utilized, the wall surfaces 32 and 34 cooperating to defineconvergent and divergent sections and a throat therebetween. Thepressurized source of sealing gas 28 is effective to provide forsupersonic flow at least in the divergent passageway section downstreamof the throat 40 and across the beam chamber 18. As is also illustratedin FIG. 1 the discharged stream is oriented generally transversely withrespect to the beam to provide a gaseous seal across the vessel opening16 and thus to prevent leakage of environmental gas into the vessel.

Although the curved supersonic stream of gas permits very low pressuresto be achieved in the flow adjacent the vessel opening 16 it is anecessary adjunct to such flow that compression and expansion waves willappear therein. These waves, or pressure disturbances, will bepropagated across the stream and some of the beneficial effects of thehigh speed low pressure supersonic flow will be lost if any compressionwaves cross the stream upstream of the vessel opening 16. In thisembodiment, the compression waves are formed only downstream of ajunction 35 on the outer wall surface 34. The compression Wavesnecessarily formed on the generally concave turning surface 34 arepostponed by means of an upstream part of said surface which issubstantially straight and which is located between the throat 40 andthe junction 35. Downstream of the junction, the surface 34 is arcuateso as to facilitate the formation of compression waves thereon, theinitial such wave being formed at the junction 35. With the design MachNo. a known factor, the initial compression Wave will be propagated fromthe junction 35 and will form a known angle with the surface 34. Thus,the junction 35 can be and is located such that the initial compressionwave passes downstream of the vessel opening 16. The initial such Waveis indicated generally in FIG. 1 by the broken line 37 originating at 35and extending angularly downstream therefrom.

Successive compression waves will of course be formed on the arcuatepart of the surface 34 downstream of the junction 35 as a resulting ofthe concave curvature of the part. These compression waves define areasof successively increasing pressure and thus tend to further accentuatethe pressure gradient across the sealing gas discharged into the beamchamber 18.

As a result of the convex curvature of the inner surface 32 downstreamof the throat 40 expansion waves will be formed thereon. The effect ofsuch Waves on the pressure at the opposite side of the passageway is notas deleterious as would be the effect of compression waves crossing thepassageway. Thus, the inner wall surface 32 is preferably convex fromthe throat 40 to the outlet 17 of the supply passageway 33 as shown inFIG. 1. At the downstream edge 38 of the inner wall surface 32, aplurality of expansion waves will be formed defining areas ofsuccessively decreasing pressure. The net effect of all of saidexpansion waves is to further accentuate the pressure gradient acrossthe sealing gas in the beam chamber 18.

The inlet 19 of the return passageway 43 is preferably of slightlylarger cross section than 'the outlet 17 of the supply passageway 33 andis preferably stepped inwardly with respect to said outlet 17 as shownin FIG. 1. In this manner use is made of the additional expansion at theedge 38 and the pressure of the sealing gas adjacent the vessel opening16 is further reduced.

By appropriate choice of a sealing gas source pressure, the pressure atthe second opening 20 can be made approximately equal to the pressure ofthe workpiece environmental gas thus minimizing mixing of saidenvironmental and sealing gas. The supersonic stream of sealing gas willthus block any flow of environmental gas into the evacuated vessel whilethe pressure gradient across the said stream permits leakage of sealinggas into the evacuated vessel to be minimized and the capacity of thehigh vacuum pump 26 to be substantially reduced. As a result of thesupersonic flow phenomenon produced by the expansion surface ordiverging wall 32 and the substantially converging wall or compressionsurface of wall 34 downstream of junction point 35, the flow crosssection along the beam axis 12 will be as follows: The expansion wavesemanating from the surface 32 and particularly from adjacent theupstream lip 38 of opening 16 provide a continually decreasing pressureregion in a downstream direction (right to left in FIGURE 1). Thus thebeam initially penetrates the cross flow in an area which is at apressure not substantially higher than that existing in the area 16,which, as stated above, is maintained at a relatively low pressure by avacuum pump 26. For the foregoing reason and since, as is well known, afluid flowing at supersonic velocity has difficulty following sharpexpansion surfaces or corners such as that presented by the upstream lip38 of opening 16, there will be little flow upwardly into region 16. Theforegoing phenomenon is explained in US. Patent No. 2,811,828, issued toG. H. McLafferty on November 5, 1957. Progressing downwardly along thebeam axis 12 from lip 38 to the region of opening 20, the pressure willon the average progressively increase. A relatively high pressure in theregion of opening results from the continued increase of pressure in thecross-flow stream resulting from the shock waves formed on and movingfrom left or right from junction point on wall 34 across the opening 20and along wall 44. The relatively high pressure in the region of opening20 caused by these shock waves will prevent gas from without the casingfrom flowing upwardly through opening 20.

The above-described pressure gradient along the beam axis from lip 38 toopening 20 caused by the expansion and compression waves in thesupersonic flow creates, in the manner explained, a relatively highpressure in the region of opening 20. Due to this high pressure, some ofthe gas being pumped through the cross-flow orifice system will beforced downwardly through opening 20. The amount of gas Which will bleedout through opening 20 is, of course, determined by the pressure in thecrossflow orifice which pressure, as is well known in the art, is afunction of the pressure of the source 28. Rather than detrimental, thisinherent loss of gas out through opening 20 provides an extremelybeneficial self-cleaning effect for the opening. That is, in the priorart, attempts at bringing a working beam out of an evacuated containerhave been plagued with difiiculties caused by splatter from theworkpiece rapidly causing clogging of the beam exit hole. With thisinvention, the bleed or selfcleaning gas flow through opening 20 tendsto force debris rising from the beam impingement point on workpiece awayfrom opening 20. This bleed flow also precipitates an added advantage ofpreventing contamination of the work since, if an inert gas is used inthe system, the surface of the workpiece will be blanketed, as is donein tungsten inert gas welding, with such gas.

The return passageway 43 preferably comprises a supersonic diffusermeans adapted to reduce the speed of the sealing gas and to thus reducethe pressure losses in conveying the gas back to the pressure source 28through the piping means 46. This minimizes the task of the pumpingmeans 28 and permits the use of a comparatively small pump or otherpressurizing means. As shown in FIG. 1 the diffuser is formed by theopposing wall surfaces 42 and 44 of said housing 30 and preferably hasan upstream convergent section and a downstream divergent sectiondefining a throat 45 therebetween. The inlet 19 of the return passageway43 comprises the inlet of the convergent section and an inner edge 39 ofsaid inlet 19 is stepped inwardly as mentioned. By a series of obliquecompression Waves in the convergent section the speed of the stream ofsealing gas is reduced with a minimum loss in stagnation pressure thuspermitting a relatively small pumping means as stated.

While the embodiment of FIGURE 1 has been described as a closed loopsystem, as will be obvious from the explanation of the embodiments ofFIGURES 2 through 4 below, the sealing gas flowing in the cross-flowsystem may be dumped into the atmosphere downstream of the beam axis.That is, it may in some cases be desirable to eliminate the supersonicdiffuser and dump the sealing gas into the atmosphere at some pointdownstream of the trailing edge of opening 20. The foregoing might bedone, for example, when an inexpensive gas is utilized.

Gaseous Seal Across Beam, Open Loop System, FIG. 2

Referring to FIG. 2, a beam generator is shown emitting a beam ofcharged particles or the like along an axis 112. That part of the beamgenerator from which the beam emanates is contained in an evacuatedvessel 122, which vessel is connected by means of a pipe 124 to a highvacuum pump 126 capable of maintaining a pressure on the order of 10-Torr in said vessel 122. The beam is concentrated by a focusing means114 to be passed through a small vessel opening 116 and thence through abeam chamber 118 and through a second opening 120 to impinge on aworkpiece 150. The beam chamber 118 is defined by a housing meansattached to the vessels exterior and adjacent said vessel opening 116,said chamber being in communication with the vessel opening at its innerend and with the second opening 120 at its outer end.

The housing means 130 may be attached to the exterior of vessel 122 asshown and is disposed between the vessel opening 116 and the workpiece150. Opposing wall surfaces 132 and 134 arranged in inner to outer orderwith respect to the vessel opening 116 at least partially define apassageway 133. The said passageway is represented in FIG. 2 as beingannular in cross sectional shape but may take various other forms solong as the outlet thereof is peripherally arranged around at least aportion of the beam chamber 118.

One end of the annular passageway 133 is connected by means of anannular plenum 113 and a pipe 115 to a pressurized source of sealing gas128, and the other end, defining an annular outlet 117, is connected toand communicates peripherally with the cylindrical beam chamber 118.

Still referring to FIG. 2, it will be seen that the passageway 133 turnsa stream of sealing gas generally towards the vessel opening 116 bymeans of a generally concave downstream portion of the outer wallsurface 134. In turning the stream a pressure gradient is achievedthereacross as previously mentioned, the lower pressure occurring inthat part of the discharged stream adjacent the vessel opening 116.

In order to further reduce the pressure of said sealing gas in the areaof the vessel opening 116 a supersonic nozzle is preferably employed toincrease the velocity of the stream. As shown, the annular wall surfaces132 and 134 cooperate to define convergent and divergent sec tions inthe direction of flow and an annular throat therebetween. When such anozzle is utilized the source of sealing gas 128 is at a pressure highenough to achieve supersonic flow at least in the divergent passagewaysection and in the beam chamber.

In this embodiment the discharged stream of sealing gas is directedgenerally obliquely with respect to the beam axis so as to have acomponent generally transverse with respect to the beam and a componentdirected outwardly through the second opening 120. Unlike the firstmentioned embodiment of the invention in which the sealing gas isrecaptured on the opposite side of the beam chamber, this embodimentrequires a continuous source of sealing gas, this stream of said gasbeing ultimately discharged from the beam chamber through the secondopening and into the workpiece environment gas as shown. The pressurerise due to obstruction of the flow of sealing gas by the environmentalgas is utilized to prevent leakage of the environmental gas into theevacuated vessel.

Although the curved supersonic stream of sealing gas permits very lowpressures to be achieved in the flow adjacent the vessel opening 116, itis a necessary adjunct to such a stream that compression and expansionwaves will appear therein. As previously mentioned, these waves orpressure disturbances will be propagated across the stream and some ofthe beneficial effects of the high speed low pressure supersonic flowwill be lost if any of the compression waves cross the stream upstreamof the vessel opening 116. Therefore, in this embodiment as in the firstmentioned embodiment of the invention, the compression waves arepreferably formed only at and downstream of a junction 135 on the outerwall surface 134. The compression waves necessarily formed on thegenerally concave wall surface 134 are delayed by means of an upstreamsubstantially straight part of said wall surface between the throat 140and the junction 135. Downstream of said junction the wall surface 134is arcuate so as to facilitate the formation of compression wavesthereon. With the design Mach No. known, the initial compression wavewill leave the surface 134 at a known angle therewith and the junction135 is so located that said initial compression wave passes downstreamof the vessel opening 116. Such a wave is indicated generally in FIG. 2by the broken line 137 originating at the junction 135.

Successive compression waves formed on the arcuate part of the wallsurface 134 define areas of successively increasing pressure and thustend to further accentuate the pressure gradient across the sealing gasdischarged into the beam chamber 118. As is well known such a successionof oblique compression waves is to be preferred over a single normalshock at the opening 120 because of the low pressure recoverycharacteristic of the latter.

Further in accord with the presently preferred practice, the inner wallsurface 132 in the divergent section of the passageway 133 is of convexcurvature so that expansion waves will be formed thereon. As in the FIG.1 embodiment, the said inner wall surface is preferably convex from thethroat 140 to the outlet 117 as shown. At the downstream edge 138 ofsaid surface 132 a plurality of expansion waves will necessarily beformed each of which defines an area of successively decreasingpressure. The net effect of all of said expansion waves is to furtheraccentuate the pressure gradient across the sealing gas discharged intothe beam chamber 118.

Gaseous Seal Around Beam, Open Loop System, FIG. 3

Referring now to FIG. 3, a beam generator 210 is shown emitting a beamof charged particles or the like along an axis 212. The part of the beamgenerator from which the beam emanates is contained in an evacuatedvessel 222, which vessel is connected by means of a pipe 224 to a highvacuum pump 226 capable of maintaining a pressure on the order of Torrin said vessel 222. The beam is concentrated by a focusing means 214 tobe passed through a small vessel opening 216 to impinge on a workpiece250 which workpiece is held in closely spaced relationship to saidvessel opening by a table 251 or the like.

Attached to the vessel 222 an forming a part thereof which defines thevessel opening 216 is an inner annular housing member 218. Said memberhas a cylindrical bore forming the opening 216 and includes an innerwall surface 232. An outer annular housing member 220 defines an outerwall surface 234 of a gas supply passageway 233.

One end of the annular passageway 233 is connected to a pressurizedsource of sealing gas 228 by the piping 215 and the other end,comprising an outlet 217, is defined by a downstream edge 236 of theouter wall surface 234 and a downstream edge 238 of the inner surface232. Said outlet 217 is adapted to discharge sealing gas around theperiphery of the beam and radially outwardly with respect theretoadjacent a workpiece 250.

Unlike the first and second mentioned embodiments in which thedischarged gas is directed into the path of the beam, this embodimentoperates not unlike an ejector in that the discharged gas creates a lowpressure about the periphery of the opening 216 and in the space betweensaid opening and the workpiece without crossing the beam itself. Thisembodiment, like that of FIG. 2,

requires a continuous source of sealing gas, there being no provisionfor recovering the gas as in the first mentioned embodiment of FIG. 1.

Referring more specifically to the passageway 233, the outer wallsurface 234 is preferably concave at a downstream portion to turn thestream of sealing gas generally towards the vessel opening 216 and tothereby achieve a pressure gradient across the discharged stream at theoutlet 217. In turning the stream towards the vessel opening the lowerpresure results in that part of the stream closest to the vessel opening216, the space between said vessel opening and the workpiece 250providing a means for communication between said stream and opening.

In order to further reduce the pressure of the sealing gas in the areaof flow which is in communication with the vessel opening, a nozzle ispreferably employed to increase the velocity of the stream. Thepresently preferred practice is to use a supersonic nozzle means, thewall surfaces 232 and 234 cooperating to define convergent and divergentsections and a throat 240 therebetween. The source of sealing gas 228 isat a high enough prsesure to achieve supersonic flow downstream of thethroat 240 in the divergent passageway section and downstream of theoutlet 217 into the space between the workpiece 250 and the lower endportion of the outer annular member 220, both of which elementscooperate to form a continuation of the passageway 233. This space orpassageway continuation is not unlike the beam chamber 218 in theprevious embodiment, FIG. 2, the stream of discharged gas being orientedgenerally obliquely as it enters said space and then dischargedoutwardly into the environmental gas as it leaves the space. Thus, thedevice is similar to the previous embodiment in that a pressure rise isachieved in obstruction of the flow of sealing gas by the workpieceenvironmental gas. Unlike the previous device, however, this embodimentdoes not require the stream to cross the beam and so avoids all beamattenuation due to the sealing gas stream.

Although the curved supersonic stream of sealing gas permits very lowpressures to be achieved in the area of flow which is in communicationwith the vessel opening, it is a necessary adjunct to such a stream thatcompression and expansion waves will appear therein. These waves, orpressure disturbances, are propagated across the stream and some of thebeneficial effects of the high speed low pressure supersonic flow willbe lost if any compression waves cross the stream upstream of that partof the flow which is in communication with the vessel opening 216.Therefore, in the present embodiment, as in the previously mentioneddevices, the compression waves are preferably formed only downstream ofa junction 235 on the outer wall surface 234. The compression wavesnecessarily formed on the generally concave surface 234 are delayed bymeans of an up stream part of the wall surface which is substantiallystraight and which extends between the throat 240* and the junction 235.Downstream of said junction the outer Wall surface 234 is arcuate os asto facilitate the formation of compression waves thereon. With thedesign Mach. No. known, the initial compression wave leaves the wallsurface 234 at a known angle therewith and the junction 235 is solocated that said wave passes downstream of the area of said sealing gasstream which is in communication with the vessel opening 216. The brokenline 237 originating at 235 and extending across the stream to theworkpiece 250 represents such an initial wave.

Successive compression waves formed on said arcuate part of the wallsurface 234 define areas of successively increasing pressure asmentioned and thus tend to further accentuate the pressure gradientacross the sealing gas discharged into the space between the workpiece250 and the member 220.

Further in accord with the presently preferred practice, the inner wallsurface 232 in the divergent section of the passageway 233 is of convexcurvature so that expansion waves will be formed thereon. At thedownstream edge 238 of said surface a plurality of expansion waves willnecessarily be formed each of which defines an area of successivelydecreasing pressure. The net efiect of this wave pattern will furtheraccentuate the pressure gradient across the sealing gas discharged intothe space between the workpiece and the annular housing member 220.

Gaseous Seal and Mechanical Seal Around Beam, FIG. 4

FIG. 4 shows an apparatus for working materials by means of a beam ofcharged particles or the like similar in most respects to thatillustrated in FIG. 3, a gaseous seal being provided around the beam. Inaddition to the gaseous seal, however, a mechanical seal 252 is alsoprovided around the beam and is disposed between the gaseous seal andthe beam.

According to presently preferred practice the mechanical seal is ofresilient material and takes an annular shape with a center hole 254 ofslightly larger size than the vessel opening 216. An outer circumference256 of the seal is of roughly the same diameter as the circular edge238a of the inner wall surface 232a. The said seal 252 is or may befixedly attached, adjacent its center hole, to the lower end portion ofthe inner annular member 218a. The outer circumference 256 of the sealrests on the upper face of the workpiece 250 and being resilient is welladapted to conform to any uneveness in the face of the workpiece. Theseal is held in contact with the workpiece at least partly by reason ofthe difference in pressure across said seal, the static pressure of thesealing gas stream past the seal necessarily exceeding the very lowpressure in the evacuated vessel 222.

As will be noted, parts generally similar to corresponding parts of theembodiment of FIG. 3 have here been given like reference numerals andsuch parts will not be described in detail. Of the corresponding partsonly the inner and outer annular members 218a and 220a differ in anymaterial respect. The inner member 218a is not directly attached to thevessel 222, and the outer member 220a is slidably received by saidvessel as shown.

It is characteristic of a flexible mechanical seal such as 252 thatoptimum sealing can only be achieved within a narrow range of angularpositioning of the seal with respect to the workpiece face. Thischaracteristic has the effect of making the distance between the face ofthe workpiece and the lower end portion of the annular member 218a acritical dimension. Not only must the workpiece 250 be in closely spacedrelationship with the housing members 218a and 220a, but the saidworkpiece must not be so close thereto as to impair the etiiciency ofthe seal.

Accordingly, biasing means are provided which hold the inner and outermembers 218a and 220a in a relatively fixed relationship to theworkpiece 250. As shown the biasing means comprise a spring 258 actingbetween the exterior of the vessel 222 and an upper end portion 221a ofthe outer member 220a, which member is fixedly attached to the innermember 218a. In operation, the use of the spring 258 makes thepositioning of the workpiece 250 with respect to the beam generatingapparatus 200 less critical. The operator merely sets the workpiececlose to the apparatus and the spring 258 will position the outer andinner members 220a and 218a in the optimum position for efficientlysealing the opening 216 from both the environmental gas and the sealinggas.

Further in the present embodiment, a second mechanical seal 260 isrequired because of the movable connection between the vessel 222 andthe outer annular member 220a. The inner annular member 218a, inconjunction with the vessel 222, defines the beam opening 216, whichopening is at very low pressure and therefore requires sealing at anyconnection where inward gas leakage is likely to occur. The slidableconnection between the vessel 222 and the member 220a is thereforefitted with a bellows type seal 260 as shown in FIG. 4.

Finally, the relative motion between the apparatus 200 to which thesource is attached and the annular housing members 218a and 220arequires a flexible hose or the like 262 connecting the source'ofsealing gas 228 to the piping 215a and the passageway 233a.

The invention claimed is:

1. Apparatus for working materials by means of a beam of chargedparticles comprising:

means for generating a beam of charged particles;

a vessel containing at least a portion of said beam generating means,said vessel defining an opening for transmission of said beam;

means for creating and maintaining a first relatively low pressure insaid vessel;

means for directing the beam out of said vessel through said opening sothat the beam will impinge on a material to be worked located outside ofsaid vessel in a region where the environmental gas is at a secondpressure greater than the said first pressure;

a source of gas under pressure; and

means connected to said pressurized source of gas for generating asupersonic stream of gas and establishing a pressure gradient betweensaid vessel opening and the environmental gas in the region of thematerial to be worked, said means thereby effecting passage of said beamfrom said vessel opening without material attenuation thereof.

2. The apparatus of claim 1 wherein the means for establishing apressure g adient comprises:

means defining a gas supply conduit having a throat therein foracceleration of gas flowing therethrough to supersonic velocity, saidconduit being connected at one end to said pressurized source of gas andhaving an outlet portion arranged to discharge a supersonic stream ofgas adjacent said vessel opening.

3. The apparatus of claim 2 wherein the gas supply conduit definingmeans comprises:

housing means defining a first opening adjacent said vessel opening anda second opening spaced outwardly from said vessel opening and alignedthere- With for passage of the beam therethrough, said housing meansserving also to define a beam chamber between said first and said secondopenings and gas supply and exit passageways communicating respectivelyat their outlet and inlet ends with said beam chamber.

4. The apparatus of claim 3 wherein the outlet and inlet ends of saidsupply and exit passageways are respectively disposed in opposingrelationship for the generally transverse flow of gas across said beamchamber.

5. The apparatus of claim 4 wherein said gas supply passagewaycomprises:

opposed inner and outer wall surfaces arranged in that order withrespect to said vessel opening, said supply passageway extendingupstream from said beam chamber in generally angular relationship withrespect to the axis of a beam passing through said aligned openings,said inner and outer wall surfaces further serving to define said throattherebetween.

6. The apparatus of claim 5 wherein:

the outer wall surface of said passageway downstream of said throatcomprises:

a generally concave portion adjacent the outlet end of said supplypassageway for turning the gas entering said beam chamber from saidsupply passageway towards said exit passageway thereby generatingcompression waves in said supersonlc stream of gas; and i said innerwall surface of said supply passageway downstream of said throatcomprises:

a generally convex portion adjacent the outlet end of said supplypassageway to provide for the formation of expansion waves in the gasleaving said supply passageway, said expansion and compression wavesestablishing a pressure gradient across the stream of gas in the beamchamber, the lower pressure being adjacent said first opening.

7. The apparatus of claim 6 wherein the generally concave portion ofsaid outer wall surface comprises:

a substantially straight wall segment adjacent said throat; and

an arcuate wall segment downstream of said straight part, obliquecompression waves being formed in said gas at and downstream of thejunction of said straight and arcuate segments, said junction being solocated that the initial compression wave extends beyond the outlet endof said gas supply passageway and across the beam chamber downstream ofsaid first opening.

8. The apparatus of claim 7 wherein said inner wall surface downstreamof said throat further comprises:

a downstream edge adjacent said first opening which presents a sharpexpansion angle to said supersonic stream of gas thereby furtherexpanding the gas adjacent said vessel opening.

9. The apparatus of claim 8 wherein said exit passageway comprises:

inner and outer opposing wall surfaces defining a convergent-divergentpassageway section in the direction of flow, said section serving toreduce pressure losses in the passageway gas.

10. The apparatus of claim 2 wherein the gas supply conduit definingmeans comprises:

housing means defining a first opening adjacent said vessel opening anda second opening spaced outwardly from said vessel opening and alignedtherewith for passage of the beam therethrough, said housing meansserving also to define a beam chamber between said first and secondopenings and a gas supply passageway communicating with said beamchamber, said passageway being arranged to extend upstream from saidbeam chamber in a direction generally oblique with respect to the axisof a beam passing through said aligned openings.

11. The apparatus of claim 10 wherein said gas supply passagewaycomprises:

opposed inner and outer wall surfaces defining a passageway which isannular in cross section and has its outlet end disposed about said beamchamber to communicate peripherally therewith, said inner and outer wallsurfaces further serving to define said throat therebetween.

12. The apparatus of claim 11 wherein:

the outer wall surface of said passageway comprises:

a generally concave wall surface downstream of said throat for turninggas entering said beam chamber from said supply passageway therebygenerating compression waves in said supersonic stream of gas; and

said inner wall surface of said supply conduit downstream of said throatcomprises:

a generally convex portion to provide for the formation of expansionwaves in the gas leaving said supply passageway, said expansion and andcompression waves establishing a pressure gradient across the stream ofgas in the beam chamber, the lower pressure being adjacent said firstopening.

13. The apparatus of claim 12 wherein said generally concave portion ofsaid outer wall surface comprises:

a straight part and an arcuate part downstream of said straight part,the junction of said straight and arcuate parts being so located thatoblique compression waves are formed commencing at said junction withthe 12 initial such wave extending across said beam chamber downstreamof said vessel opening.

14. The apparatus of claim 13 wherein said convex inner wall surfacefurther comprises:

a downstream edge adjacent said vessel opening which edge presents anabrupt convex turning angle to the gas leaving said passageway wherebyto further expand the flow past said vessel opening and to therebyreduce the pressure of the gas and minimize leakage of the same into thevessel.

15. The apparatus of claim 2 wherein the gas supply conduit definingmeans comprises:

housing means defining a gas supply passageway connected with saidpressurized source of gas and having an outlet portion arranged toestablish a flow of gas which circumscribes a beam of charged particlespassing through said vessel opening, said gas flow extending outwardlyto the surface of the material to be worked thereby inhibiting flow ofenvironmental gas to the region between said vessel opening and the areato be worked.

16. The apparatus of claim 15 further comprising:

a mechanical seal afiixed to housing means at a point between saidvessel opening and the outlet end of said supply passageway andextending from said housing means to the surface of a material to beworked with the beam whereby said seal serves to isolate said vesselopening from said sealing gas thereby further minimizing leakage of saidgas into said vessel.

17. The apparatus of claim 16 wherein said seal comprises a flexibleannular member, wherein said housing means is adapted for movementtoward and away from the material to be worked, and wherein a biasingmeans is provided for urging said housing means toward the material tobe worked thereby maintaining the seal in effective sealing engagementbetween the housing means and the material being worked.

18. The apparatus of claim 15 wherein said gas supply passagewaycomprises:

opposed inner and outer wall surfaces defining a passageway arranged todischarge gas radially outwardly with respect to the axis of the beam,said inner and outer wall surfaces further serving to define said throattherebetween.

19. The apparatus of claim 18 wherein said gas supply passageway isannular in cross section and discharges a stream of gas peripherallyaround said vessel opening.

20. The apparatus of claim 19 wherein said gas supply passagewaydownstream of said throat comprises:

a pair of oppositely disposed wall surfaces being arranged in inner andouter order with respect to said vessel opening and being generallyconvex and concave respectively for the formation of expansion andcompression waves in the gas discharge from said passageway.

21. Apparatus for transmitting a beam of electrons from a low pressureto a gaseous environment without material attenuation thereofcomprising:

means for generating a beam of charged particles;

a vessel containing at least a portion of said beam generating means,said vessel defining an opening for transmission of said beam;

means for creating and maintaining a pressure less than atmospheric insaid vessel;

means for directing the beam out of said vessel through said openingwhereby the beam may impinge upon a material to be worked locatedoutside of said vessel in a gaseous atmosphere where the pressure isgreater than that maintained in said vessel;

21 source of gas under pressure;

housing means abutting said vessel and defining a first opening adjacentsaid vessel opening and a second opening spaced outwardly from saidvessel opening and aligned therewith for passage of the beam there- 13through, said housing means serving also to define a beam chamberbetween said first and second openings and a gas supply orifice in thewall of said chamber; and

means defining a gas supply passageway having its inlet end connected tosaid pressurized source of gas and having its outlet end connected tosaid supply orifice, said passageway having a throat therein foracceleration of gas flowing therethrough from said source to supersonicvelocity, said passageway further being contoured downstream of saidthroat so as to impart a change in direction to the supersonic stream ofgas and thereby generate compression and expansion Waves and establish apressure gradient across the gas in the beam chamber, the lower pressurebeing adjacent said first opening.

22. Apparatus for Working materials by means of a beam of chargedparticles comprising:

means for generating a beam of charged particles;

a vessel containing at least a portion of said beam generating means,said vessel defining an opening for transmission of said beam;

means for creating and maintaining a pressure less than atmospheric insaid vessel;

means for directing the beam out of said vessel through said openingwhereby the beam may impinge on the material to be worked locatedoutside of said vessel in a gaseous atmosphere where the pressure isgreater than that maintained in said vessel;

a source of gas under pressure;

means defining a gas supply passageway having a throat therein foracceleration of gas flowing therethrough to supersonic velocity, saidpassageway having its inlet end connected to said pressurized source ofgas and having its outlet end arranged to discharge said supersonicpassageway gas adjacent said vessel opening in such a manner that itcircumscribes a beam passing through said vessel opening and impingingupon the material to be worked, said gas flowing outwardly to thesurface of the material to be worked and having a pressure gradientthereacross whereby a low pressure region circumscribed by said gas iscreated between said vessel opening and the desired point of beamimpingement on the material to be Worked.

References Cited by the Examiner UNITED STATES PATENTS 2,554,236 5/51Bernard 219- 2,587,331 2/52 Jordan 21975 2,590,084 3/52 Bernard 219722,686,860 8/54 Buck et al 21975 2,769,079 10/56 Briggs 219-75 2,771,56811/56 Steigerwald.

2,806,124 9/57 Gage 21975X 2,824,232 2/58 Steigerwald.

2,899,556 8/59 Schopper et a1.

2,907,704 10/59 Trump.

2,922,869 1/60 Giannini et al.

RICHARD M. WOOD, Primary Examiner.

JOSEPH V. TRUHE, Examiner.

1. APPARATUS FOR WORKING MATERIALS BY MEANS OF A BEAM OF CHARGEDPARTICLES COMPRISING: MEANS FOR GENERATING A BEAM OF CHARGED PARTICLES;A VESSEL CONTAINING AT LEAST A PORTION OF SAID BEAM GENERATING MEANS,SAID VESSEL DEFINING AN OPENING FOR TRANSMISSION OF SAID BEAM; MEANS FORCREATING AND MAINTAINING A FIRST RELATIVELY LOW PRESSURE IN SAID VESSEL;MEANS FOR DIRECTING THE BEAM OUT OF SAID VESSEL THROUGH SAID OPENING SOTHAT THE BEAM WILL IMPINGE ON A MATERIAL TO BE WORKED LOCATED OUTSIDE OFSAID VESSEL IN A REGION WHERE THE ENVIRONMENTAL GAS IS AT A SECONDPRESSURE GREATER THAN THE SAID FIRST PRESSURE; A SOURCE OF GAS UNDERPRESSURE; AND MEANS CONNECTED TO SAID PRESSURIZED SOURCE OF GAS FORGENERATING A SUPERONIC STREAM OF GAS AND ESTABLISHING A PRESSUREGRADIENT BETWEEN SAID VESSEL OPENING AND THE ENVIRONMENTAL GAS IN THEREGION OF THE MATERIAL TO BE WORKED, SAID MEANS THEREBY EFFECTINGPASSAGE OF SAID BEAM FROM SAID VESSEL OPENING WITHOUT MATERIALATTENUATION THEREOF.